Field of the Invention
The present invention relates to an imprint apparatus, and a method of manufacturing an article using the imprint apparatus.
Description of the Related Art
Recently, the micropatterning of semiconductor devices has advanced, and imprint techniques of coating a substrate such as a wafer with a resist and curing the resist with an original (mold) being pressed against the resist are beginning to be used as semiconductor device manufacturing methods. A photo-curing method is one imprint technique. In an imprint apparatus using the photo-curing method, a region (shot region) as a pattern formation region on a substrate is first coated with a photo-curing resist. Then, alignment correction of the substrate and a mold is performed using a correction mechanism for correcting a mold size. Subsequently, the mold is pressed against the resist. After that, the resist is cured by ultraviolet irradiation, and the mold is released from the resist. Consequently, resist patterns are formed on the substrate. Japanese Patent No. 4185941 has disclosed an imprint apparatus for the photo-curing method.
In the imprint apparatus, patterns already formed on a substrate and a mold are aligned by using the die-by-die alignment method. When pressing the mold against each shot region in the die-by-die alignment method, a substrate mark and mold mark are observed using a TTM (Through The Mask) scope for directly measuring the marks through the mold, and a shift amount between them is measured and corrected. In the die-by-die alignment method, however, correct alignment is sometimes impossible because a mark shift caused by a process factor such as a decrease in amount of a film such as an underlayer is observed for each shot region.
By contrast, the global alignment method is most frequently used in conventional exposure apparatuses using a photolithography technique of transferring patterns of an original onto a substrate via a projection optical system. In the global alignment method, marks in several typical shot regions are measured, and a global index (coefficient) for obtaining the position of each shot is calculated by processing the measurement results. Then, each shot region is aligned based on the global index. In the global alignment method, alignment is performed using the same index. By conducting a sampling test on several shot regions in a post-process, therefore, it is possible to determine the quality of all shot regions of the substrate, and increase the productivity. It is also possible to avoid (reduce) the influence of an abnormal position shift caused by a process factor by properly selecting sample shot regions. This increases the stability of overlay accuracy. In the conventional exposure apparatus, the global alignment method is performed using an off-axis scope (OAS) installed in a position far from an exposure position. In the imprint apparatus, however, the global alignment method using the TTM scope is also possible. When adopting the global alignment method using the TTM scope, the OAS is no longer necessary, so the driving range of a substrate stage can be reduced. This makes it possible to decrease the size of the whole apparatus and reduce the cost.
When performing the global alignment method using the TTM scope in the imprint apparatus, measurement is performed by spacing a mold and substrate apart from each other to some extent. This spacing is normally about a few ten μm. This measurement performed with the mold and substrate being not in contact with each other but spaced apart from each other is called proximity measurement. If the optical axis of the TTM scope inclines to the driving direction of an imprint head, the imprint head shifts from the optical axis of the TTM scope while the head is driven by a few ten μm, even when imprinting is performed in a position aligned by global alignment. That is, imprinting is performed in a position different from an original position where a mark is seen. This decreases the overlay accuracy.
This similarly applies to the die-by-die alignment method. The die-by-die alignment method includes a contact method in which alignment is performed using the TTM scope with a mold and substrate being in contact with each other, a proximity method in which alignment is performed using the TTM scope before a mold and substrate are brought into contact with each other, and a method combining these two methods. In the contact method, an inclination difference between the optical axis of the TTM scope and the imprint head driving direction poses no problem. While a mold and substrate are in contact with each other, however, when a resist is filled in a mark position, the TTM scope is sometimes unable to measure the mark due to the refractive index of the resist. Also, while a mold and substrate are in contact with each other, the TTM scope can measure a shift amount between the mold and substrate, but there are some limitations, for example, a substrate stage cannot be moved very much. This makes the proximity method effective in the die-by-die alignment method as well. As in the global alignment method, however, the inclination difference between the optical axis of the TTM scope and the imprint head driving direction decreases the overlay accuracy when imprinting is performed.